In the oil and gas industry, work strings including various downhole devices are often extended downhole within drilled boreholes to perform various wellbore operations. Downhole devices, such as sliding sleeves and ball valves, include primary sealing elements that serve to isolate fluids within or without the work strings. Placing these downhole devices in a downhole environment subjects them to elevated pressures and extreme pressure differentials that threaten the integrity of the primary sealing elements.
For instance, sliding sleeves are typically used in completion assemblies to occlude flow ports that communicate with a surrounding subterranean formation. Subterranean formations can exhibit pressures near 10,000 psi or more, and when the sliding sleeve is in a closed position, a pressure differential is generated across the sliding sleeve between the subterranean formation and the interior of the completion assembly. The primary sealing elements of the sliding sleeve are able to resist fluid migration through the flow ports, and thereby effectively isolate the fluids in the subterranean formation from the interior of the completion assembly. Upon moving the sliding sleeve to an open position, however, the flow ports become exposed and the pressure differential will attempt to equalize at an extremely high rate. Such rapid pressure equalization can have a detrimental impact on the primary sealing elements. For example, rapid pressure equalization can potentially blow out the primary sealing elements or cause seal erosion over time. As a result, the integrity of the primary sealing elements is often compromised and any subsequent use of the downhole device may not be optimal.
In an effort to mitigate the effects of rapid pressure equalization, some sliding sleeve assemblies incorporate a slot defined in the seal bore between the primary seals. While shifting the sliding sleeve between closed and open positions, the slot becomes exposed for a brief period of time to facilitate a small amount of pressure equalization. Another method of mitigating the effects of rapid pressure equalization uses an equalizing port provided adjacent the sliding sleeve. The equalizing port often contains a small ball bearing or a poppet valve that is propped off seat by the sliding sleeve when the sliding sleeve is shifted between closed and open positions. These methods, however, complicate the design of the sliding sleeve assembly and introduce additional leak paths into the interior of the completion assembly.